Transient Analysis of Acoustically Derived Pressure and Rate Data

Abstract

A pressure-buildup test conducted on a sucker-rod pumping well is often distorted by long-duration wellbore storage. In fact, this distortion could be so severe that even a week's shut-in period may not allow a semilog analysis. A longer shut-in period becomes economically discouraging because of lost production.Low energy and low transmissivity in the reservoir, coupled with increased fluid compressibility, contribute to this long-duration storage phenomenon. One way of reducing the storage effect clearly lies in the simultaneous analysis of downhole pressure and flow rate, estimated from casinghead pressure and rising annular liquid-level measurement made by acoustic well sounding (A WS). Ascertaining the quality of the indirectly measured pressure and rate data constitutes one of the objectives of this study.Several methods exist to translate the A WS measurement to downhole pressure and rate data for the subsequent transient analysis. We show that even an empirical hydrodynamic correlation provides satisfactory transient-pressurelflow-rate data for convolution and deconvolution analyses for moderate pumping-liquid columns. When long annular liquid columns are encountered, translating the A WS measurement with a mechanistically based hydrodynamic model appears to be a prudent approach.Interpretation of several transient tests show that automated convolved-type-curve or history matching of field data is a powerful tool for reservoir-parameter (total mobility, skin, fracture half-length, and storage coefficient) estimation. Use of downhole rate for the convolved type-curve matching reduces the variable storage coefficient by several orders of magnitude, thereby enhancing the quality of the estimates. Deconvolution of downhole pressure and rate data and the pressure-derivative approach significantly aided in well/reservoir flow-model identification.A simple algorithm for computing the Laplace transform of the wellbore pressure for an infinite-conductivity vertically fractured well in an infinite reservoir is developed in this work for a rapid, iterative-type computation used in automated convolved-typecurve analysis.

Horizontal Well Test Analysis System

“…• before well shut-in( tD~tDs ) P WDVF = sqDVPWDH (14) where PWDVF can be evaluated in real number domain with Stehfest inversion algorithm.…”

New Well-Testing Methods for Rod-Pumping Oil Wells — Case Studies

“…These occurrences would compromise performance of the pressure transient analysis. Soliman presented the use of superposition in pumping well test analysis 1 , Kabir introduced the use of deconvolution 2 and a segmental analysis approach by using automatic convolved type-curve methods 3 to improve the analytical capabilities of existing well-test analysis techniques.…”